The proposed research project is a surgically-oriented experimental animal study designed to determine the feasibility of a mechanical heart-lung system, functioning acceptably as a chronic (up to two weeks) substitution for the natural heart and lungs of awake, standing sheep. Substitution of the mechanical pump-oxygenator system for the natural heart and lungs will be accomplished by two different technques, and the results compared. In one group of animals, cannulation of both vena cava and the ascending aorta will be carried out, with institution of cardiopulmonary bypass. Total resection of both lungs and the heart will then be accomplished, continuing the cardiopulmonary bypass as chronic cardiopulmonary substitution. In the second group of experiments, total effective respiratory and cardiopulmonary hemodynamic function will be performed by the substitute mechanical heart-lung system, while the natural heart and lungs remain anatomically in situ but do not contribute to effective respiratory or cardiopulmonary hemodynamic functions. Both groups of animals will be extensively instrumented and will be observed continuously during recovery from anesthesia and thereafter in the awake, standing, and moving condition in the ICU. Physiologic hemodynamic, respiratory, hematologic, and biochemical responses will be monitored. Mortality, morbidity, and duration of life in the two groups will be evaluated and compared. Data will be utilized to evaluate the feasibility of total substitution of a mechanical cardiopulmonary system for the natural heart and lungs on a chronic basis in the awake, standing animal.